Homopolar Generator.pdf

A HOMOPOLAR GENERATOR by Bruce DePalma

BACKGROUND

The present invention relates to an electric generator.

The generator described herein is referred to as a quadrapole

generator because of the four distinct magnetic poles involved in

the machine.

Homopolar generators produce low voltages at high

currents. In the later 1800’s these unipolar generators were used

in metal reduction and plating applications where high currents

are required. In the early 1900’s however, the development of

commutated DC and AC generators which could develop higher

voltages at lower operating speeds led to the decline in use of

homopolar generators, except for specialised applications.

Another prior art generator involves the combination of

two one piece homopolar generators similar to that designed by

Michael Faraday in 1831 and mounted in common on a central

supporting conducting shaft. This generator was constructed with

magnet poles aligned in opposition so that they were voltage

additive between two current collector rings encircling the centers

of the tandem rotating magnets. The current generated by this

generator ows radially inward in a conducting disc located

centrally within and co-axially disposed within one magnet through

the connecting axle and then radially outward in a disc co-axially

disposed within the second magnet. The mechanism of voltage

generation in this generator was similar to that in the previously

described one piece Faraday homopolar generator wherein the

magnetic ux lines within the magnets are perpendicular to the

conducting disc co-rotating with and centrally disposed within

each permanent magnet assembly.

PRIOR ART

In 1831 Michael Faraday performed the initial experiments

which resulted in the discovery of the dynamo. In one of

his experiments a copper disc was secured to a cylindrical

magnet with paper intervening the two. The poles of the magnet

were aligned along the axis of the copper disc. Wires of a

galvanometer brushed the centre and circumference of the

copper disc respectively. It was discovered that upon rotation

of the copper disc and magnet, an electrical potential was

created between the terminals of the galvanometer. This simple

construction is known as a homopolar generator. Importantly,

this experiment revealed that a potential difference was created

across the copper disc when it was rotated through a magnetic

eld, irrespective of whether the magnet was rotated with the

copper disc or remained stationary.

Another early generator was the two piece design by

Faraday where a conducting disc is revolved adjacent to the

poles of xed magnets.

One disadvantage of this generator is that the current

output is limited by the diameter of the supporting axle. If the

axle is larger, it is necessary to have larger holes in the magnets

through which reverse ux may pass. The necessity for the

hole through the magnets and the reverse ux problem reduces

magnet strength and voltage.

The copper discs of this generator were subdivided into two

spirals to produce a self magnetising effect with current withdrawal

which counteracted partially the high internal resistance of the

long current path through the two copper spirals and the axle. The

50mm diameter shaft limited current output to four kiloamperes.

Above this current level excessive heating would occur.

Another disadvantage of this prior art generator is that the

dumb-bell shaped rotor lacks rigidity compared with the rotor of

the present invention to be described below. This affects ease of

balancing the rotor.

A Homopolar Generator

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current collectors co-operating with a rotor body wherein the

rotor body comprises; at least one electrically conductive

member,

a central zone between end zones,

at least~two axially aligned magnets, arranged so that like

poles of the magnets oppose to produce ux lines which

pass through and exit the central zone of said rotor body in

a direction radial to the axis of rotation;

wherein the magnets in polar opposition rotate with the

conductive member or members and wherein the north/

south polar alignment of each magnet is axial; and electrical

contacts proximate each end zone and an electrical path

or paths proximate the radial extremities of the rotor

and between each contact formed by said electrically

conductive member or members.

Preferably there is one electrically conductive member

comprising a cylindrical tube and the magnets are permanent

magnets which are permanently xed with respect to the tube.

The poles of the magnets are preferably orientated co-axially

with the axis of the tube and the tube is preferably rotated at high

speed.

Alternatively, the performance characteristics of the

generator may be achieved by use of alternative structural

arrangements which receive and retain the magnets and other

rotor components. For example, it would be possible to use an

array of radially disposed conductors such as rods providing

electrical paths connecting electrical contacts on the rotor

Alternatively, the generator may comprise concentric cylinders or

a nest of cylindrical tubes whose axes are parallel.

According to another embodiment there is provided an

electric generator as hereinbefore described including an

electrically conductive compensation tube provided about said

central zone and spaced apart therefrom, an end of said

compensation tube being electrically connected to the contact

adjacent thereto, the other end of said compensation tube being

electrically connected to a generator output terminal.

The advantages of the homopolar generator according to the

present invention include the following:

a solid magnet across the frill internal diameter of the

tube providing higher and uniform magnetic eld and the

elimination of current ow through the magnet and an

increased current carrying capacity now only limited by the

size of the current collectors.

In another broad form the present invention comprises;

a rotor for use with a generator as hereinbefore described,

the rotor comprising; a rotor body comprising; at least one

electrically conductive member, a central zone between

end zones,

at least two axially aligned magnets arranged so that like

poles of the magnets oppose to produce ux lines which

DESCRIPTION OF INVENTION

According to the present invention there is provided a

single piece homopolar generator which has one moving part,

the rotor and in which the desired electrical potential is produced

without the mutual interaction of a second member (stator). This

generator includes an electrically conductive member such as

a cylindrical tube having two magnets therein which, when the

generator is in operation, rotate with the tube. The cylindrical

version of this generator, known as a Quadrapole, is not

an immediately apparent development of the original Faraday

‘one-piece’ axially rotated magnet experiment since the vector

directions of the (radial) magnetic ux lines and axially owing

electrical current are interchanged in their respective directions

in comparison to the previously described Faraday Disc

experiment.

The one-piece, rotor only version of what is presently

known as a cylindrical homopolar generator has not hitherto

previously been known.

Throughout the specication the term ‘homopolar’ can be

taken to mean the repulsion of like magnetic elds, i.e. N-N

or S-S which can alter the direction of magnetic ux lines and

produce a radial pattern in the central zone of the rotor.

Within the last ten years certain materials such as rare

earth, Neodymium-Iron-Boron (Nd2Fe14B), and Samarium-

Cobalt (SaCo) permanent magnets, and Niobium-Tin or

Niobium-Titanium superconductive magnet wire have become

available. With these materials it becomes practical to fabricate

magnetic structures impossible to realise with iron and copper

wire. The conguration of the present invention exploits the

advantages that modern magnetic materials provide .

It is an object of the present invention to provide an

improved generator or to at least provide the public with a useful

choice.

In one broad form of the invention there is provided an electric

generator comprising:

a single piece homopolar generator for use alone or in

combination with like or known generators comprising:

when the rotor is in use pass through and exit the central

zone of said rotor body in a direction radial to the axis of

rotation;

wherein the magnets in polar opposition rotate with the

conductive member or members and wherein the north/

south polar in alignment of each magnet is axial; and

electrical contacts proximate each end zone and an

electrical path or paths proximate the radial extremities of

the rotor between each contact formed by said electrically

conductive member or members.

In an alternative form, the invention comprises;

a current collector for use with a generator as hereinbefore

described, the current collector comprising;

a two part body one of which pans is detachably attached

to the other part, wherein when the two parts are attached,

a central bore is formed which receives a rotor,

means located at least partially within said bore for creating

a seal between the rotor and the outside of the bore,

wherein said means forms a circumferential recess within

the bore in which an electrically conductive material is

located and which is in electrical contact with electrical

contacts on a rotor in the generator, wherein, the space

between the base of the recess and the electrical contacts

of rotor is lled with liquid metal or eutectics providing an

electrical path between the rotor and the current collector.

Preferably the electrical contacts are machined into the rotor and

comprise a circumferential ring on each end zone, providing an

electrical connection between the surface of the cylindrical tube

and the conductive liquid metal or eutectics.

In a inher form according to the system aspect the present

invention comprises:

a system for generating electricity using a single piece

homopolar generator; the system comprising;

the single piece generator, having one moving part, the

rotor, and in which the desired electrical potential is

produced without mutual interaction of a stator,

a power source to drive the generator,

a eld of energy inuence within which the generator is

situated and with which the generator interacts,

wherein the interaction between the generator and the eld

inuences the output of the generator by supplementing

energy input to the generator from said power source.

A Homopolar Generator

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one-piece cylindrical homopolar generator has not previously

been known.

Because of the existence of a region of zero radial magnetic

eld in a zone encircling the center of a cylindrical permanent

magnet, i.e. the neutral zone, current extraction from the rotating

member is taken at this point. Current extraction by means

of a liquid metal sliding contact in this zone eliminates any

electro-magnetic forces which might act to disturb the liquid

metal contact during current extraction. A zone of zero magnetic

ux also eliminates electrical currents circulating transversely

through the conductive body of a current collector because of

inhomogeneities in voltage across the width of the liquid metal

sliding contact.

With the Quadrapole, the magnets are arranged NSSN

or SNNS and the fact that the magnetic ux lines emerge

radially from the center of the conducting cylinder is because of

the mutual repulsion of opposing directions of like (homopolar)

force.

In the conventional two-piece cylindrical homopolar

machine, magnetic ux lines are caused to emerge radially from

the central voltage generation segment of the cylindrical rotating

member by xed iron pole pieces which encircle the rotating

cylinder and form part of a stator structure which closes the

magnetic ux paths in xed external loops back to each axle

of the machine. The two piece closed path construction makes

no use of the mutually repulsive effect of homopolar magnetic

elds because in the closed path construction the magnetic eld

internal to the cylinder is directed to ow radially outward by low

magnetic reluctance external pole pieces.

Without the provision of external pole pieces and a closed

magnetic ux path, the attainable magnetic eld strength within

such a machine would be so low as to render the machine not

suitable for commercial application. Rare earth high strength

permanent magnets make it possible to obtain high strength

and useful radially directed magnetic ux lines without closed

magnetic ux paths. The radially directed ux arises from mutual

repulsion of homopolar uxelds.

The key requirements of the cylindrical one-piece homopolar

generator as herein described are that all parts of the rotor

including the magnets must rotate together and there is no

closure of the magnetic ux paths by xed ferromagnetic yokes,

- stators.

If the permanent rare-earth magnets are replaced with

super-conducting electrical solenoidal coils, the coils must rotate

with the cylinder. The magnetic elds produced when they are

cooled and energised must be poled NSSN or SNNS and

the spacing of the coils adjusted to produce radial ux lines

perpendicular to the central voltage producing segment, (of

the rotating conductive cylinder enclosing and supporting the

magnet solenoids). The mutual repulsion of homopolar ux elds

is employed to create radially diverging ux lines in the central

zone.

A rotor may be constructed of multiple concentric conducting

cylinders. In the zone of zero or low magnetic ux pertaining

to the region encircling the centers of rare-earth magnets or

super-conducting solenoids, multiple sliding liquid metal contacts

may be established thus enabling a series connection of the

portions of the concentric conducting cylinders in the voltage

generating region between the opposing poles of the rotating

magnets contained within the nested cylinders. Voltage addition

by connecting a series of concentric conducting cylinders in a

The present invention in all its forms will now be described in

more detail according to a preferred but non-limiting embodiment

and with reference to the accompanying illustrations wherein:

A Homopolar Generator

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Figure 1: shows a long sectional view through a generator rotor

according to a preferred embodiment;

Figure 2: shows an exploded view of the generator incorporating

the rotor of gure 1 according to a preferred embodiment

of the invention;

Figure 3: shows an isometric exploded view of one current

collector for use with the generator;

Figure 4: shows an assembled view of the current collector of

gure 3,

Figure 5: shows the rotor of gure 1 seated in part of current

collectors and showing the relationship of the rotor to

the electrical contacts and seals.

Figure 6: shows a long section through the generator rotor of

gure ~ with lines of magnetic ux indicated,

Figure 7: shows an embodiment of the rotor according to a

preferred embodiment of the present invention including

magnetic compensation,

Figure 8. shows an isometric view of the completed generator with

output terminals according to a preferred embodiment

of the invention, and

Figure 9: shows the generator of gure 8 from a rear view driven

via a drive belt by a drive motor.

The magnets are oriented so that their like poles oppose (in

this case the north poles) resulting in magnetic ux lines being

directed radially outwardly from central zone 14 of cylindrical

tube 3 . Throughout the specication the term ‘central zone’ can

be taken to mean that region in the centre of the rotor wherein

the output voltage is generated when the rotor is rotated. A cavity

15 is formed between two shaped cast iron pole pieces 20 and

21 between magnets 12 and 13 .

As well as having a central zone 14 , cylindrical tube 3

includes end zones 18 and 19 wherein the central zone 14 is

disposed between the end zones.

Referring to gure 2 there is shown an exploded view of

the generator of gure 1 including the rotor 2 of gure 1 , current

collectors 22 and 23 and their interrelationship with the cylindrical

tube 3 .

Figure 2 also shows connected to electrically conductive

cylindrical tube 3 end caps 6 and 7 terminating in rotor shaft ends

8a and 8b respectively.

Current collectors 22 and 23 both of which are identical

are located at contacts 32 and 33 in end zones 18 and 19

respectively of cylindrical tube 3 . Each collector is located along

cylindrical tube 3 in a neutral region of each end zone in a

ux eld where the concentration of ux is low. As current

collectors 22 and 23 are identical, only current collector 22 will be

described in detail and with reference to gure 3 below to avoid

duplication.

As the rotor of the generator I is rotated, a voltage potential

develops between contacts 32 and 33 . Power output is drawn

from the generator via the two current collectors 22 and 23 . The

mercury provides the electrical contact between the cylindrical

tube 3 and current collectors 22 and 23 which are in electrical

contact with output terminals 24 and 25 (see gure 8 ). It has

been found that using the pole conguration shown in gure 1

that 3 to 4 times the voltage output of a standard homopolar

generator may be obtained using magnets having the same eld

strength.

Referring now to gure 3 there is shown an exploded

isometric view of a typical current collector. Figure 3 shows an

enlargement of the current collector 22 of gure 2 comprising

two parts 27 and 28 which preferably are symmetrical about

their plane of separation and which together form a contact

body housing 26 (see gure 4 ). Body parts 27 and 28 are

preferably manufactured from a high conductivity material eg.

copper. To form current collector 22 each of parts 27 and 28

which include semi circular bores 29a and 29b respectively

receive substantially semi circular and preferably plastic sealing

elements 30a , 30b , 30c and 30d which when in situ and mated

together form circular recess 31 (see gure 4 ). In use, recess 31

receives liquid mercury which provides the electrical contact with

contact 32 on cylindrical tube 3 . Contact 32 rotates in circular

recess 31 . Body parts 27 and 28 are mated together by means

of bolts or locking screws 34 and 35 .

Referring now to gure 1 there is shown a sectional view

of a rotor 2 for use with a generator 1 (see gure 2 ) according

to a preferred embodiment of the invention. Rotor 2 comprises

an electrically conductive cylindrical tube 3 which may include

end plates 4 and 5 . End plates 4 and 5 each preferably comprise

an aluminium disc. Fixed to the ends of cylindrical tube 3 and

covering plates 4 and 5 respectively are non magnetic stainless

steel end caps 6 and 7 . End caps 6 and 7 terminate in shaft ends

8a and 8b respectively. End caps 6 and 7 are preferably afxed

to the cylindrical tube 3 by means of screw threads 6a and 7a

located on end caps 6 and 7 respectively. Alternatively, end caps

6 and 7 may be xed via an internal thread (not shown) on inner

surface 3a of cylindrical housing 3 or xed with a glue or friction

tted. The electrically conductive tube 3 of rotor 2 may comprise

as an alternative hollow members such as but not limited to a

sphere or cube. Shaft ends 8a and 8b may be integral with or

are detachably connected to end caps 6 and 7 and are co-axial

with cylindrical tube 3 . Rotor shaft ends 8a and 8b are, when in

situ, surrounded by bearing assemblies 9a and 9b (see gure 2 )

respectively allowing free rotation of the cylindrical tube 3 upon

rotation of rotor shaft 8 . Once bearings 9a and 9b (see gure 2)

are tted to the rotor shaft ends 8a and 8b , the bearings are

contained within stationary supports 10 and 11 (see gure 2 ).

Cylindrical tube 3 rotates freely about its axis when driven via

shaft ends 8a or 8b . Fixed to cylindrical tube 3 are permanent

magnets 12 and 13 which rotate with the cylindrical tube 3 when

the generator operates.

Figure 4 shows the current collector 22 of gure 3

assembled. When body parts 27 and 28 are mated together a

seal is created by plastic seal 30 formed by sealing elements

30a , 30b , 30c and 30d thereby preventing the escape of liquid

mercury during operation of the generator. It will be appreciated

that plastic seal 30 can be an integral member as an alternative

to formation by separate elements. There is a small clearance

between sealing elements 30a , 30b , 30c , 30d and the rotor 2 .

Screw threads are machined on the sealing lands 58 , 59 , 60 , 61

(see gure 1 ) of the cylindrical tube 3 , so that any leakage of

mercury is returned when the rotor is rotating to recess 31 - the

electrical contact zone.

As an alternative to use of liquid metal contacts, electrical

brushes which are widely used in electrical machinery may be

used. However, the generator, according to the present invention

produces low voltage at very high currents which is generaijy

unsuitable for solid sliding contacts. The preferred contacts

are conducting liquid metals such as mercury or eutectics

such as sodium-potassium or gallium-indium. The use of liquid

metal electrical contacts gives the advantage of lower electrical

resistance, lower mechanical friction and low wear.

Electrical contacts 32 and 33 are machined into the

cylindrical tube 3 . Preferably a number of annular ridges 32a and

33a may be formed on contacts 32 and 33 respectively. Contacts

32 and 33 are when surrounded by current collectors 22 and

23 separated by a very small clearance between the conductive

surface of recess 31 (in the case of contact housing body 26 ).

There is a corresponding arrangement in contact assembly 23 .

Preferably that clearance for each contact is 0.5mm or less.

Each of current collectors 22 and 23 include capillary lines.

As the capillary line arrangements for current collectors 22 and

23 are the same, the following description will relate to the

capillary line for current collector 22 shown assembled in gure

4 . Referring to gure 3 it can be seen that body part 28 of

current collector 22 includes mercury reservoir 44 which feeds

into capillary line 42 with ow of liquid metal into recess 31 being

controlled by means of valve 46 . In use, rotor 2 is rotated and

then liquid metal is introduced from reservoir 44 via the capillary

line 42 to the space between the circumferential contact 32 (see

gure 1 ) and recess 31 of current collector 22 (see gure 3 ).

Centrifugal forces and viscous drag cause liquid metal to

be taken up on the contacts 32 and 33 of cylindrical tube 3 to

form a circumferential ring of liquid metal bead encircling those

contacts. Thus, for current collector 22 mercury is in contact

with the surfaces within recess 31 of contact body housing 26 .

Similarly for contact assembly 23 . Because the liquid metal bead

is held in place by a combination of centrigal and viscous

forces the clearance between contact 32 and recess 31 can

be quite large (for instance; 2mm). Once the cylindrical tube is

rotating and the liquid metal has been introduced, the apparatus

will operate equally well either horizontally or vertically. For

satisfactory operation the liquid metal should wet the inner

surfaces of recess 31 . In the case of mercury, to achieve proper

amalgamation it is preferred that a process is employed to

remove oxide from the surface of the body parts 27 and 28 prior

to introduction of the mercury.

A Homopolar Generator

5/7

Referring to gure 5 there is shown the rotor 2 of gure 1

seated in part of current collectors 22 and 23 . It can be seen that

contacts 32 and 33 locate in recesses 31 and 37 respectively.

Recess 31 is formed by plastic seal elements 30a , 30b and

recess 37 is formed by seal elements 38a and 38b . Seal

elements 30a , 30b , 38a and 38b engage respectively sealing

lands SB, 59 , 60 and 61 which have helical threads which urge

any mercury that escapes recesses 31 and 37 back into those

recesses when the rotor rotates.

Referring now to gure 6 there is shown a long section

view of the rotor 2 of gure 1 showing the disposition of the

ux lines relative to the cylindrical tube 3 . Cylindrical tube 3

is shown including permanent magnets 12 and 13 . Magnets

12 and 13 are preferably permanent magnets and may either

be conventional magnets, rare earth metal magnets or super

conducting magnets. The magnets 12 and 13 may each be

formed from a plurality of magnetic elements or other magnetic

material. As cylindrical tube 3 is preferably formed of a high

strength, high electrical conductivity copper alloy the cylindrical

tube can be rotated at very high speeds. The polar oppositition

conguration of magnets 12 and ] 3 produce ux lines which

pass through and exit the central zone of cylindrical tube 3 in a

direction that is perpendicular to the axis of the cylindrical tube

3 in central zone 14 . From gure 6 it can be seen that there is

a concentration of radial ux in central region 14 as depicted by

ux lines 39 . Flux lines 40a , b, c and d are concentrated in end

zones 18 and 19 as shown.

Rotation of the conductive cylindrical tube 3 with the

magnetic ux generates a potential difference between contacts

32 and 33 (refer gure 1 ). The electric potential between terminals

32 and 33 is given by the relationship

E = 1O - 8 .v. Bn / l

where:

E is the potential difference between the contacts 32 and

33 in volts,

Bn is the ux density (in Gauss) normal to the surface of

cylindrical tube 3 , i.e. acting radially to the axis of rotation

of the rotor.

l is the distance in cm between contacts 32 and 33 ; and

v is the tangential velocity of the surface of cylindrical tube

3 in cm/second.

Accordingly, I will effectively be the length of cylindrical

tube 3 adjacent poles 16 and 17 .

As the potential difference is proportional to the tangential

velocity of the cylinder it is preferable that the cylindrical tube 3 be

built as large as possible to achieve optimal output voltage, and

be rotated as fast as possible, for example, up to 100,000 rpm or

beyond if physical limits permit.

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